Effects of Erlong Zuoci Pill (耳聋左慈丸) and Its Disassembled Prescriptions on Gentamicin-induced Ototoxicity Model in vitro

Objective：To study the effects of Erlong Zuoci Pill（耳聋左慈丸,ELZCP）and its disassembled prescriptions on gentamicin（GM）-induced ototoxicity model in vitro.Methods：After the spiral organ of cochleae of newborn mice（postnatal days：2-3）cultured for 24 h,GM alone or combined with water extracting-alcohol precipitating solution of ELZCP or with its disassembled prescriptions was added.Hair cells were observed under a fluorescence microscope after TRITC-phalloidin staining,and the cochlear hair cell loss rate was calculated by counting the whole cochlear hair cells and analyzed by whole cochlear hair cells analyzing software.Results： GM induced cochlear outer hair cells（OHCs）and inner hair cells（IHCs）injuries in a dose-dependent manner, and they were significantly different as compared with those in the normal control group（P〈0.05,P〈0.01）. ELZCP at the concentration of 0.003-3 mg/mL could decrease the hair cells loss induced by the 0.3 mmol/L GM （P〈0.05,P〈0.01）,the effects was in a dose-dependent manner,and the concentration of 0.3 mg/mL showed the optimal protective effect.For the ELZCP disassembled prescriptions,Liuwei-Dihuang could decrease OHC loss rate than that in the 0.3 mmol/L GM model group（P〈0.05）,but the OHC loss rate was still higher than that in the ELZCP group（P〈0.01）,which indicated that the protective effect of hair cells by Liuwei-Dihuang was not better than that of ELZCP.Poria decreased OHC loss rate from 72.1%±3.7%to 58.8%±8.2%（P〈0.05）. Conclusions：ELZCP could play a role in antagonizing the injury of cochlear hair cells induced by GM ototoxicity, and its disassembled prescriptions,Liuwei-Dihuang was the main component to protect the cochlear hair cells from GM-induced ototoxicity,and Magnetitum combined with Radix Bupleurui could strengthen the action of the whole prescription; Poria could reduce GM-induced OHC loss.

Mitochondrial DNA mutations associated with aminoglycoside induced ototoxicity

Aminoglycosides(Am An) are widely used for their great efficiency against gram-negative bacterial infections. However, they can also induce ototoxic hearing loss, which has affected millions of people around the world. As previously reported, individuals bearing mitochondrial DNA mutations in the 12 S rRNA gene, such as m.1555A>G and m.1494C>T, are more prone to Am An-induced ototoxicity. These mutations cause human mitochondrial ribosomes to more closely resemble bacterial ribosomes and enable a stronger aminoglycoside interaction. Consequently,exposure to Am An can induce or worsen hearing loss in these individuals. Furthermore, a wide range of severity and penetrance of hearing loss was observed among families carrying these mutations. Studies have revealed that these mitochondria mutations are the primary molecular mechanism of genetic susceptibility to Am An ototoxicity, though nuclear modifier genes and mitochondrial haplotypes are known to modulate the phenotypic manifestation.

Gene expression in cisplatin ototoxicity and protection with p53 inhibitor

Cisplatin damages cochlear hair cells and spiral ganglion neurons through cell death signaling pathways that are not fully understood. We used focused apoptosis gene microarrays to study early changes in gene expres- sion in cochlear cultures from P3 neonatal rats treated with cisplatin (0.2 mM). After 12 hours of cisplatin treat- ment, more than 50% of the 96 genes on the array showed a significant decrease in expression, consistent with widespread cell death. However, after 3 hours of cisplatin treatment, 10 genes showed significant increase in ex- pression in total cochlear tissue. In experiments with subsets of cochlear tissues, at 3h, cisplatin induced increased expression of 12 genes in the cochlear sensory epithelium (basilar membrane) and 11 genes in the spiral ganglion (tissue of Rosenthal’s canal, containing the spiral ganglion). These included pro- and anti-apoptotic genes in- volved in the p53 signaling pathway, TNF receptor family, NF-kappaB pathway, death domain family, death effec- tor domain family, Bcl-2 family, CARD family, TRAF family, and GTP signal transduction. Although the changes in gene expression showed an overlap between basilar membrane and spiral ganglion, other changes, which may reflect the unique response of each tissue, were also observed. Pifithrin-α blocked cisplatin-induced up-regulation of genes in the p53 signaling pathway when assayed by both superarray and real time PCR. The data add to our understanding of the involvement of p53 in cisplatin-induced ototoxicity and otoprotection, conferred by the p53 inhibitor Pifithrin-α.

Partial Protection by Lipoic Acid Against Carboplantin-induced Ototoxicity in Rats

Objective To investigate the alterations in auditory brainstem evoked responses (ABRs) and the changes of carboplatin-induced ototoxicity in the cochlear oxidant/antioxidant systems and otoprotection by an antioxidant lipoate. Methods Male wistar rats were divided into four groups and treated as follows: 1) vehicle (saline) control, 2) carboplatin (256 mg/kg, i.p.), 3) lipoate (100 mg/kg, i.p.), 4) lipoate + carboplatin. Post-treatment ABRs were performed after four days and rats were sacrificed with their cochleae harvested and analyzed. Results Carboplatin significantly elevated ABR threshold above the pretreatment thresholds. Lipoate+carboplatin treated rats showed decreased elevation of hearing threshold. Carboplatin significantly depleted cochlear reduced to oxizized glutathione (GSH/GSSG) ratio, whereas lipoate+carboplatin treatment increased GSH/GSSG ratio. Carboplatin significantly decreased cochlear copper zinc-superoxide dismutase (CuZn-SOD), catalase (CAT), glutathione peroxidase (GSH-Px), glutathione reductase (GR) and glutathione-S-transferase (GST) activities and enzyme protein expressions and a significant increase in Mn-SOD activity, protein expression and malondialdehyde (MDA) level. Cochlear antioxidant enzyme activities, enzyme protein expressions and MDA level were partially restored in lipoate+carboplatin treated rats, compared to carboplatin alone. Conclusion Carboplatin-induced ototoxicity is related to impairment of cochlear antioxidant system and otoprotection conferred by lipoate is associated with partial sparing of the cochlear antioxidant defense system.

Ligustrazine facilitates hair cell regeneration in the cochlea following gentamicin ototoxicity

BACKGROUND： Ligustrazine （tetramethylpyrazine） decreases ototoxicity induced by gentamicin and facilitates hair cell regeneration and repair, but the precise mechanisms remain controversial.OBJECTIVE： To explore the protective effects of ligustrazine on gentamicin ototoxicity by determining heat shock protein 70 mRNA and protein expression in the cochlear stria vascularis of guinea pigs at different time points.DESIGN, TIME AND SETTING： The randomized, controlled study was performed at the Laboratory of Physiology, Shenyang Medical College of China in 2007.MATERIALS： Ligustrazine parenteral solution （Qiqihar Pharmaceutical Factory, China） and gentamicin sulfate （Shenyang First Pharmaceutical Factory, China） were used in this experiment.METHODS： White guinea pigs with red eyes were randomly intraperitoneally administered gentamicin sulfate injection ＋ saline, gentamicin sulfate injection ＋ ligustrazine, and ligustrazine ＋ saline, respectively.MAIN OUTCOME MEASURES： Auditory brains tern response threshold was measured. Immunohistochemistry, in situ hybridization, and image analyzing techniques were utilized to determine heat shock protein 70 mRNA and protein expression in cochlear stria vascularis of guinea pigs.RESULTS： Following gentamicin ototoxicity, the auditory brainstem response threshold increased, peaked on day 3, and then decreased with increased time after drug withdrawal. The auditory brainstem response threshold was significantly diminished following ligustrazine intervention, but recovered to normal on day 30 （P〉0.05）. Heat shock protein 70 expression also increased, peaked on day 3, and then decreased in the cochlear stria vascularis of guinea pigs following gentamicin ototoxicity. Ligustrazine intervention resulted in decreased heat shock protein 70 expression in the cochlear stria vascularis, which recovered to normal on day 14. Heat shock protein 70 mRNA expression increased in the cochlear stria vascularis following gentamicin ototoxicity, but ligustrazine intervention resulted in decreased levels. CONCLUSION： Ligustrazine significantly ameliorated gentamicin ototoxicity by reducing heat shock protein 70 mRNA and protein expression in the cochlear stria vascularis.

Calpain mediated cisplatin-induced ototoxicity in mice

Ototoxic drug-induced apoptosis of inner ear cells has been shown to be associated with calpain expression. Cisplatin has severe ototoxicity, and can induce cochlear cell apoptosis. This study assumed that cisplatin activated calpain expression in apoptotic cochlear cells. A mouse model of cisplatin-induced ototoxicity was established by intraperitoneal injection with cisplatin （2.5, 3.5, 4.5, 5.5 mg/kg）. Immunofluorescence staining, image analysis and western blotting were used to detect the expression of calpain 1 and calpain 2 in the mouse cochlea. At the same time, the auditory brainstem response was measured to observe the change in hearing. Results revealed that after intraperitoneal injection with cisplatin for 5 days, the auditory brainstem response threshold shifts increased in mice. Calpain 1 and calpain 2 expression significantly increased in outer hair cells, the spiral ganglion and stria vascularis. Calpain 2 protein expression markedly increased with an increased dose of cisplatin. Results suggested that calpain 1 and calpain 2 mediated cisplatin-induced ototoxicity in BALB/c mice. During this process, calpain 2 plays a leading role.

Ototoxicity induced by kanamycin in iron-deficient young rats

Using auditory electrophysiological,histopathological,enzymehistochemical and scanning electron microscopic techniques,we observed thechanges of function and structure of cochlea in iron-deficient growing rats receiv-ing kanamycin intramuscularly.The results showed that at an equal dose ofkanamycin,hearing loss and hair cell damage were more serious,and incidence ofhearing loss was much higher in iron-deficient rats than in normal rats.Theinhibition of succinate dehydrogenase activity of cochlea induced by interaction ofkanamycin and iron deficiency was more obvious than that by either one of them.Iron deficiency can increase the sensitivity of cochlea to kanamycin.The resultsindicated that iron deficiency may be one of the reasons for high incidence ofototoxic deafness in children,and it should be cautious when using such drugs inchildren with iron-deficient anemia.

Ototoxicity of povidone-iodine——A case report

Objective: The ototoxicity of povidone-iodine has been documented in animal studies. However, there is limited evidence of these ototoxic effects in humans. This is the first report to show the ototoxic effects of povidoneiodine in a human subject.Patient: A 36-year-old woman came to our hospital complaining of left unilateral persistent hearing loss. One month before presentation, her child had accidentally struck her on her left ear. She applied approximately three drops of povidone-iodine(10% weight/volume) into her left auditory canal. Immediately after application, she felt severe pain and vertigo. An audiogram revealed severe left unilateral sensorineural hearing loss. Magnetic resonance imaging showed mild enhancement of the left vestibule and basal turn of the left cochlea.Conclusions: Even a single application of povidone-iodine could cause significant hearing loss and disequilibrium. It should, therefore, be used with caution.

Ototoxicity of styrene

Styrene is extensively used in industry,but its ototoxicity,in particular in the pregnant female and the offspring,is still not well understood.In the current study,young adult male rats and pregnant female rats were exposed to styrene by gavage at different doses.The young adult male rats received a total of 12g/kg styrene within different periods (800 mg/kg/day for 5 days/week for 3 weeks,400 mg/kg/day for 5 days/week for 6 weeks,200 mg/kg/day for 5 days/week for 12 weeks,and 100 mg/kg/day for 5 days/week for 24 weeks) and the pregnant female rats received styrene at a dose of 400 mg/kg/day for 5 days/week for 6 weeks starting from the gestation day-4.Hearing loss and hair cell loss were assessed 5 days after the styrene treatment in the young adult male rats and in the mother rats.The cochlear impairments in the rat pups were examined 2 months after their birth.The styrene exposure caused hearing loss and hair cell loss starting from the mid-frequency region in the third row of outer hair cells (OHCs) and the impairments appeared to be related to the dosing level in each single day.Significantly,the styrene exposure to the pregnant rats interfered with auditory functional development of their fetus,leading to a deficit of cochlear amplification,although the OHCs appeared to develop well.The results indicate that a short-term high-level styrene exposure may be more ototoxic than a long-term low-level exposure for a similar total styrene dose and the styrene in the pregnant woman’s body may interfere with auditory development of their fetus.

Mitochondrial DNA Mutations Associated with Aminoglycoside Ototoxicity

The mitochondrial 12S rRNA has been shown to be the hot spot for mutations associated with both aminoglycoside-induced and non-syndromic hearing loss. Of all the mutations, the homoplasmic A1555G and C1494T mutations at a highly conserved decoding region in the 12S rRNA have been associated with aminoglycoside-induced and non-syndromic hearing loss in many families worldwide. The A1555G or C1494T mutation is expected to form novel 1494C-G1555 or 1494U-A1555 base-pair at the highly conserved A-site of 12S rRNA. These transitions make the secondary structure of this RNA more closely resemble the corresponding region of bacterial 16S rRNA. Thus, the new U-A or G-C pair in 12S rRNA created by the C1494T or A1555G transition facilitates the binding of aminoglycosides, thereby accounting for the fact that the exposure to aminoglycosides can induce or worsen hearing loss in individuals carrying these mutations. Furthermore, the growth defect and impairment of mitochondrial translation were observed in cell lines carrying the A1555G or C1494T mutation in the presence of high concentration of aminoglycosides. In addition, nuclear modifier genes and mitochondrial haplotypes modulate the phenotypic manifestation of the A1555G and C1494T mutations. These observations provide the direct genetic and biochemical evidences that the A1555G or C1494T mutation is a pathogenic mtDNA mutation associated with aminoglycoside-induced and nonsyndromic hearing loss. Therefore, these data have been providing valuable information and technology to predict which individuals are at risk for ototoxicity, to improve the safety of aminoglycoside antibiotic therapy, and eventually to decrease the incidence of deafness.

Ototoxicity of vancomycin in guinea pigs

Objective: To study the effect of vancomycin (V) with multiple intravenous injections on the inner ear of albino guinea pigs. Methods: Three groups of animals were injected with vancomycin hydrochloride (54, 108, 216 mg/kg respectively once a day for 14 d). Two groups were treated with gentamycin (GM) (80 mg·kg -1 ·d -1 ) and saline respectively as control groups. Auditory brainstem responses (ABR) and the duration of post-rotatory nystagmus (PRN) were measured before and after administration. Surface preparation and scanning electron microscopy (SEM) of the cochlea were performed for histological examination. Results: In V 54, 108 mg/kg group, similar to saline control, there was 0-1.1 dB of threshold shift. In V 216 mg/kg group, average hearing loss was 1.0-5.7 dB immediately after administration and 1.3-3.8 dB after 14 d, which was significantly lower than those in GM control group. As the saline control, no significant difference was found in PRN in all V groups before and after treatment; while in the GM group, PRN decreased significantly after treatment. Morphological evaluation demonstrated that in all V and saline animals there was no obvious missing of outer and inner hair cells and SEM showed normal surface morphology. In the GM group, there was 10%-30% of outer and inner hair cells lost in the basal turn. Conclusion: The ototoxicity of vancomycin is absent or minimal after multiple introvenous administration within this dose range.

ULTRASTRUCTURAL OBSERVATIONS ON REGENERATING HAIR CELLS IN THE CHICK BASILAR PAPILLA FOLLOWING AMINOGLYCOSIDE OTOTOXICITY

Newly hatched chicks were injected with so mg/(kg' d) of gentamycin sulfate (GM )for 10 days. After 18st injection, animals were killed on survival days 3,6 .9 and 12. The chick basilar papillae (BP) were observed by transmission electron microscopy (TEM ). The results sho've'Ithat regenerated hair cells were erupted to the hasal membrane surrace in the early phase. The cytoplasm of these regenerated hair cells was heavily stained an contained numerous mitochondria. Afterseveral days, stereocilia appeared. When stereocilis bundles were rormed and cuticular layer was integrated, hasal nerve terminals were round. The results suggested that regenerating hair cells 'veredirectly produced on the hasal membrane surface following gentamycin induced ototoxlcity and thenI,roliferated and developed Into mature normal hair cells.

长爪沙鼠不同感音神经性耳聋模型的建立及比较

目的利用不同的耳毒性药物建立长爪沙鼠感音神经性耳聋模型,并对3种模型进行比较分析,为感音神经性耳聋的研究提供精准的动物模型。方法选择长爪沙鼠,建立硫酸卡那霉素和呋塞米联用(KM+Fur)、新霉素(Neo)及哇巴因(Oua)3种耳毒性药物的感音神经性耳聋模型,通过听性脑干反应(ABR)和耳蜗组织形态学检测,比较分析不同耳毒性药物的损伤特点。结果KM+Fur造模后,与对照组(14.00±1.80)相比,该组(71.00±5.26)长爪沙鼠的听力阈值显著上升,耳蜗HCs大量损伤,而SGNs无明显损伤;Neo造模后,与对照组相比,40 mmol·L^(-1) Neo仅影响沙鼠高频32 kHz时听力阈值(60.00±8.66),无明显的组织学改变;而100 mmol·L^(-1) Neo组的沙鼠各频率听力阈值均显著上升,且耳蜗HCs及SGNs均严重受损;Oua造模后,1 mmol·L^(-1) Oua和10 mmol·L^(-1) Oua均可引起沙鼠各频率听力阈值显著上升,但损伤范围不同,10 mmol·L^(-1) Oua使HCs和SGNs均严重受损,而1 mmol·L^(-1) Oua仅造成耳蜗SGNs损伤。结论利用KM+Fur可建立长爪沙鼠HCs特异性受损的感音神经性耳聋模型;40 mmol·L^(-1) Neo可建立高频区听功能损伤的感音神经性耳聋模型;利用100 mmol·L^(-1) Neo和10 mmol·L^(-1) Oua可以建立长爪沙鼠HCs和SGNs均受损的感音神经性耳聋模型;利用1 mmol·L^(-1) Oua可以建立长爪沙鼠耳蜗SGNs特异性受损的耳聋模型。

铁死亡在感音神经性耳聋中的研究进展

感音神经性耳聋(sensorineural hearing loss,SNHL)是目前人类最常见的致残性疾病之一,主要表现为耳蜗毛细胞和(或)螺旋神经元损伤所导致的永久性听力损失,而铁死亡是最近才发现的一种调节性细胞死亡形式。迄今为止,铁死亡已被证明参与了许多疾病的病理生理机制,如神经退行性病变、癌症和肾脏疾病等。目前,有相关研究报道铁死亡可能参与了SNHL的发生发展过程。我们就铁死亡机制的研究进展进行综述,阐述其在SNHL中的研究现状及应用前景,为SNHL进一步的研究和治疗提供新思路。

甘草酸抑制C57BL/6J小鼠耳蜗炎症减轻顺铂诱导的耳毒性

目的:探讨甘草酸(glycyrrhizic acid,GL)在小鼠中是否具有抵抗顺铂(cisplatin,CDDP)耳毒性的作用及其分子机制。方法:雄性C57BL/6J小鼠分为5组:对照(control)组、5%DMSO组、CDDP(4 mg/kg)组、CDDP+低剂量(50 mg/kg)GL组和CDDP+高剂量(100 mg/kg)GL组,每组14只。采用听性脑干反应(auditory brainstem response,ABR)检测不同组小鼠听力变化;HE染色观察小鼠耳蜗血管纹形态学变化;伊文思蓝(Evans blue,EB)染色观察血管纹血迷路屏障(blood-labyrinth barrier,BLB)通透性变化;免疫组化技术检测耳蜗血管纹毛细血管内皮细胞间黏附连接蛋白VE-cadherin和紧密连接蛋白ZO-1的表达和分布;ELISA和免疫荧光技术检测炎症因子白细胞介素1β(interleukin-1β,1L-1β)和肿瘤坏死因子α(tumornecrosis factor-α,TNF-α)表达变化。结果:(1)CDDP组小鼠各频率ABR波形紊乱,听力阈值显著增高,I波潜伏期延长(P<0.05);CDDP+GL组小鼠各频率ABR波形分化良好,听力阈值显著下降,I波潜伏期缩短(P<0.01)。(2)HE染色中CDDP组小鼠血管纹形态紊乱,空泡增多;GL减轻了CDDP诱导的血管纹损伤。(3)EB染色显示,CDDP导致小鼠BLB通透性增加(P<0.01),而GL改善了CDDP诱导的BLB通透性变化(P<0.01)。(4)免疫组化结果显示,CDDP组小鼠VE-cadherin和ZO-1表达下降(P<0.01);CDDP+GL组小鼠VE-cadherin和ZO-1表达升高(P<0.01)。(5)ELISA和免疫荧光结果显示,CDDP组小鼠IL-1β和TNF-α表达增加(P<0.01);CDDP+GL组小鼠IL-1β和TNF-α表达下降(P<0.01)。结论:GL通过抑制CDDP引起的炎症,降低小鼠耳蜗BLB的通透性,从而起到减轻CDDP引起的耳毒性作用。

丹参素钠对顺铂耳毒性抑制作用的实验研究

目的探讨丹参素钠(SDSS)对顺铂耳毒性的抑制作用。方法选取HEI-OC1细胞系构建顺铂诱导的损伤模型,确定顺铂在24 h对HEI-OC1细胞的50%最大抑制浓度(IC50),基于该模型在小分子化合物库中筛选具有保护作用的药物。在HEI-OC1细胞模型和小鼠耳蜗外植体毛细胞顺铂损伤模型中,检测SDSS对毛细胞存活率和凋亡水平的影响。采用超氧化物阴离子荧光探针(DHE)染色检测SDSS对顺铂诱导的HEI-OC1细胞氧化应激水平的影响并选用药物N-乙酰半胱氨酸(NAC)作为阳性对照。结果从210种FDA批准的小分子化合物中筛选出具有显著保护作用的药物SDSS,SDSS预处理可有效抑制顺铂诱导的HEI-OC1细胞凋亡、活性降低以及细胞内活性氧(ROS)升高,其最佳浓度为200μmol/L。此外,SDSS可抑制顺铂对耳蜗基底膜外植体毛细胞的损伤。结论SDSS可能通过抑制毛细胞内ROS升高并抑制细胞凋亡,从而发挥对顺铂所致耳毒性的抑制作用。

OTOTOXIC EFFECTS OF CARBOPLATIN IN ORGANOTYPIC CULTURES IN CHINCHILLAS AND RATS

Carboplatin, a second-generation platinum chemotherapeutic drug, is considerably less ototoxic than cisplatin. While common laboratory species such as mice, guinea pigs and rats are highly resistant to carboplatin ototoxicity, the chinchilla stands out as highly susceptible. Moreover, carboplatin causes an unusual gradient of cell death in chinchillas. Moderate doses selectively damage type I spiral ganglion neurons (SGN) and inner hair cells (IHC) and the lesion tends to be relatively uniform along the length of the cochlea. Higher doses eventually damage outer hair cells (OHC), but the lesion follows the traditional gradient in which damage is more severe in the base than the apex. While carboplatin ototoxicity has been well documented in adult animals in vivo, little is known about its in vitro toxicity. To elucidate the ototoxic effects of carboplatin in vitro, we prepared cochlear and vestibular organotypic cultures from postnatal day 3 rats and adult chinchillas. Chinchilla cochlear and vestibular cultures were treated with carboplatin concentrations ranging from 50 μM to 10 mM for 48 h. Consistent with in vivo data, carboplatin selectively damaged IHC at low concentrations (50-100 μM). Surprisingly, IHC loss decreased at higher doses and IHC were intact at doses exceeding 500 μM. The mechanisms underlying this nonlinear response are unclear but could be related to a decrease in carboplatin uptake via active transport mechanisms (e.g., copper). Unlike the cochlea, the carboplatin dose-response function increased with dose with the highest dose destroying all chinchilla vestibular hair cells. Cochlear hair cells and auditory nerve fibers in rat cochlear organotypic cultures were unaffected by carboplatin concentrations <10 μM; however, the damage in OHC were more severe than IHC once the dose reached 100 μM. A dose at 500 μM destroyed all the cochlear hair cells, but hair cell loss decreased at high concentrations and nearly all the cochlear hair cells were present at the highest dose, 5 mM. Unlike the nonlinear dose-response seen with cochlear hair cells, rat auditory nerve fiber and spiral ganglion losses increased with doses above 50 μM with the highest dose destroying virtually all SGN. The remarkable species differences seen in vitro suggest that chinchilla IHC and type I SGN posse some unique biological mechanism that makes them especially vulnerable to carboplatin toxicity.

Ototoxic effects of mefloquine in cochlear organotypic cultures

Mefloquine is a widely used anti-malarial drug. Some clinical reports suggest that mefloquine may be ototoxic and neurotoxic, but there is little scientific evidence from which to draw any firm conclusion. To evaluate the ototoxic and neurotoxic potential of mefloquine, we treated cochlear organotypic cultures and spiral ganglion cultures with various concentrations of mefloquine. Mefloquine caused a dose-dependent loss of cochlear hair cells at doses exceeding 0.01 mM. Hair cell loss progressed from base to apex and from outer to inner hair cells with increasing dose. Spiral ganglion neurons and auditory nerve fibers were also rapidly destroyed by mefloquine in a dose-dependent manner. To investigate the mechanisms underlying mefloquine-induced cell death, cochlear cultures were stained with TO-Pro-3 to identify morphological changes in the nucleus, and with carboxyfluorescein FAM-labeled caspase inhibitor 8, 9 or 3 to determine caspase-mediated cell death. TO-Pro-3-labeled nuclei in hair cells, spiral ganglion neurons and supporting cells were shrunken or fragmented, morphological features characteristic of cells undergoing apoptosis. Both initiator caspase 8 (membrane damage) and caspase 9 (mitochondrial damage), along with executioner caspase 3, were heavily expressed in cochlear hair cells and spiral ganglions after mefloquine treatment. These three caspases were also expressed in support cells, although labeling was less widespread and less intense. These results indicate that mefloquine damages both the sensory and neural elements in the postnatal rat cochlea by initially activating cell death signaling pathways on the cell membrane and in mitochondria.

LOWER DOSE OF AMINOGLYCOSIDE OTOTOXIC EXPOSURE CAUSES PRESYNAPTIC ALTERATIONS ASSOICATED WITH HEARING LOSS

Objective To study presynaptic alternations of cochlear ribbons arising from aminoglycoside ototoxic stimuli in C57BL/6J mice. Methods Animals were injected with low dose gentamicin (100 mg/kg/day) for 14 days, From the 14th to 28th days, the mice were maintained free of gentamicin treatment. Immunohisto-chemistry labeling was employed to trace RIBEYE, a major presynaptic componment of ribbon synapses. RIBEYE/CtBP2 expression levels were assessed and compared with hearing threshold shifts. Auditory func-tion was assessed by auditory brainstem responses. The stereocilia of outer hair cells (OHCs) and IHCs was examined by scanning electron microscopy (SEM). Results Hearing thresholds were elevated with peak hearing loss observed on the 7th day after gentamicin exposure, followed by improvement after the 7th day. RIBEYE/CtBP2 expression directly correlated with observed hearing threshold shifts. Strikingly, we did not see any obvious changes in stereocilia in both OHCs and IHCs until the 28th day. Mild changes in stereocil-ia were only observed in OHCs on the 28th day. Conclusions These findings indicate that presynapse co-chlear ribbons, rather than stereocilia, may be sensitive to aminoglycoside ototoxic exposure in mice cochle-ae. A pattern of RIBEYE/CtBP2 expression changes seems to parallel hearing threshold shifts and suggests presynaptic response properties to lower dosage of aminoglycoside ototoxic stimuli.

耳毒性物质复合噪声致听力损失的研究进展

耳毒性物质与噪声是导致感音神经性耳聋的两类重要因素,影响日益严重。日常环境中影响更为严重和常见的是多因素的联合暴露,致使听力损失逐年提高。本文就耳毒性物质复合噪声致听力损失的研究进展进行文献综述,就耳毒性物质与噪声分类及介绍、复合听力损失流行病学研究、动物实验与机制分析、防治研究进行介绍,总结现有研究成果、不足及未来方向,对于了解复合听力损失现状,指导防治及下一步研究方向具有重要意义。